Phase shifting network



Jan. 10, 1939.

W. VAN B. ROBERTS PHASE SHIFTING NETWORK Filed March 16, 1936 2 Sheets-Sheet l INVENTOR w. vm ROBERTS ATTORNEY.

Jan. 10, 1939.

w. VAN BA ROBERTS 2,143,386

PHASE SHIFTING NETWORK Filed March 16, 1936 040 o/e AMM/HER 0R FREQUENCY Mm r/gL/ER our/ur cour/waz .00mn/AL INVENTOR.

w. VAN RoERTs ATTORNEY.

l Patented im. 1o, 1939 2,143,386

UNETED STATES PATENT CFFICE amazes PHASE smr'rmG NETWORK Walter van B. Roberts, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 16, 1936, Serial No. 69,105

15 Claims. (Cl. 179-171) This invention relates to a novel phase shifting ance z and its secondary coupled to the control method and new and improved phase shifting grid and cathode of a tube I0. networks adapted to change the phase without Throughout this specification ideal transaltering the magnitude of an input alternating formers will be used to indicate in a simple fash- 5 current or voltage. The invention is characterion means for providing the voltage transformat ized by the fact that the amount of phase shift tion required, although it will be obvious to anyis determined by the transconductance of one or one skilled in the art that in many cases the more electron discharge devices forming part of same results may be obtained from more practical the network. structures. For example, if in Figure 1 im- 10 An important feature of the phase sluiting pedance e is a pure inductance, then a coil con- 10 networks of this invention is that any number nected between grid and filament may be couof network sections may be connected in cascade pled directly to z so as to give a grid excitation with the result that the total phase shift' is inexactly equal to the voltage drop across z procreased in proportion to the number of sections vided that the mutual inductance is equal to the 1:, used. self inductance of z. With this explanation it is 15 In the drawings, not considered necessary to discuss in each of Figure 1 shows a network which produces the following figures the possible alternatives for phase shift and also amplitude change in applied the transformer means shown. alternating voltages, Transformer T applies to the grid of tube I0 u Figure 2 shows a network which produces a a voltage ei-ez where e2 is the voltage at the 20 phase shift and an amplitude change in applied terminals 3 and 4 at the output end of the netalternating voltages. The -network of Figure 2 work and e1 is the input voltage. The anode to is a modification of the network of Figure 1, cathode space of the tube l0 shunts the line as Figure 3 shows a network which produces shown at the output terminals. 'Ihe transcon- 25, phase shift without amplitude change in applied ductance of the tube may be represented by g'. 25 alternating voltages. It is readily demonstrated that the iterative ad- Figure 3a shows a plurality of networks, of the mittance of the ir-terminal structure of Figure 1 nature of the network in Figure 3, in cascade is equal to the transconductance of the tube I0, with means for controlling a characteristic of a e. g., equal to o. Therefore, if an impedance 30 network, of an admittance g is connected to the output 80 Figure 4 illustrates a network which also proterminals as shown in Figure 1, the current and duces phase shift without amplitude change in voltage relations within the network will be the the applied voltages, same as though the network Were connected to Figure 5 shows a method for utilizing a vacan infinite series of other and similar networks. 3;, uum tube to provide an adjustable admittance With the understanding that the network is ter- $5 fof terminating the networks of the prior ilgminated by its iterative admittance as above exures, piained, it is easily shown that the ratio of the Figure 6 ShOWS a network adapted t0 be used output voltage e2 to the input voltage e1 is l-eg. without any terminating load for producing since g is a real quantity 1t fouows that if z is phase shift Without amplitude change in alterimaginary the Output voltage between points 3 o ating voltages y and 4 is shifted in phase and also is altered in Figure 7 is 9' network adapted to ne used with magnitude by the network as compared to the out a' terminating 10nd for prodnning phase snm' input voltage at points I and 2. The relation in nlternn'nng current voltages wltnont changing between the network admittance the tube trans- 4.-,` the amplitude thereof, conductance, and the terminating impedance will 45 Figure 8 shows one manner in which the arrangement of Figure 7 may be connected in practice between a source of alternating voltage and now be set forth more fully by reference to Figure l of the drawings. Here e1 is input voltage; u1 i1l is the input current; (e1-ez) is the voltage :,0 a 1Eliniiezxnifiixi); niv more particularly to Figure 1, between the grid and cathode of the tube l0, in 50 points l and 2 represent input terminals of a this case, furnished by T. Hence, the current network across which alternating potentials from through the anode t0 Cathode impedance Of tube any source of amplitude e may be impressed, I0 equals (e1- eng where g isthe trans-conduc- T represents an ideal one-to-one transformer tance of tube I0. e2 is the voltage at the outts having its primary winding coupled to animpedput terminals. Now let gt represent any teru terminals or the network. Then p gz en=1-(e1-ea)g since the current through the terminating conductance gt must be the volts across it times its conductance. From the last we solve for e: and substitute in the ilrst giving 1 E 6i l+l'(x) equals input conductance at terminals l, 2.

Now if we make m=0 we have From the same equations by eliminating i; and setting g=g we nd Figure 2 shows a similar network where the grid voltage is again equal to ei-ea but the conductance of tube I0 is shunted across the input terminals of the network instead of the output terminals as in Figure 1. In this case also the iterative admittance is equal to g but in this case the ratio of e2 to e1 equals Here again we have not only a phase shift but also an amplitude change occurring in the alternating potentials in the network.

Figure 3 shows a network having characteristics similar to the characteristics of the networks of Figures l and 2. The network of Figure 3 is obtained by connecting the output oi the network (which does not include 9) oi Figure 1 to the input of the network of Figure 2 with its terminating impedance y, and then combining the two tubes which fall in parallel into a single tube l0 having its grid excited with the sum of the two grid voltages of the separate tubes of the prior networks. In Figure 3 this again results in applying to the grid of the tube I0' a voltage equalto the difference between the input voltage e1 and output voltage e: of the network. As was to be expected, since the networks of both Figs. 1 and 2 possess the same iterative admittance, the network of Fig. 3 will also have this same iterative admittance g. When terminated by this admittance the ratio of output voltage to input voltage 'I'his ratio is seen to be the product of the corresponding ratios in Fig. 1 and Fig. 2, but this ratio has the interesting and useful property that its absolute value is always unity so long as the product zg is purely imaginary. It does, however,

` indicate a phase shift which is twice the angle whose tangent is the absolute value of zg. That is, ii we vary g for example, from zero to innity. the phase e2 will change from being equal to the phase of e1 around to being opposite to the phase of e1.. It will, of course, be understood that as we change the value of g for the tube Ill'in the network we must simultaneously alter the terminating conductance of the network so as to maintain the behavior of the system in accordance with the equations and statements given heretofore. If morephase shift is desired, several sections such as described may be cascaded. For example, several of the networks shown in Fig. 3 (exclusive of their terminating impedance a) may a,14a,sse

be cascaded as shown in Fig. 3a and terminated by an impedance as shown in Fig. 5. In this case modulating potentials may be applied in phase as shown to the tube structures in each stage. Then the phase shift accomplished will be in accordance with the control potentials.

Fig. 4 shows a phase shifting network obtained by connecting the output of the network oi' Fig. 2 to the input of the network of Fig. 1 and combining the impedances z of said networks and the transformers T of said networks into a single impedance 2z and a single transformer 'Ik which impresses on the grids of tubes l0" and i0' apotential equal to one-half the diilerence between the inputpotential e1 and output potential e: of the composite network. 'I'he behavior oi' this network is identical in every way with that of Figure 3. It will be noticed that if a number oi sections like Figure 3 are connected together, the resulting structure will bejidentical, except at the ends, with the structure obtained by connecting together a number of sections of networks o! the type shown in Figure 4 after simplification in the way of coalescing parallel .tubes or the like, has

' been carried out.

In the preceding discussion it has been assumed that the phase shifting network section or series of sections has been terminated by an admittance which is maintained at the same value as the transconductance of each of the tubes in the phase shifting network. I will now describe a novel network terminating impedance, and in doing so will refer to the circuit of Figure 5.

Figure 5 shows how a tube 2li identical with the tubes used in the phase shifting sections of the prior figures may be connected to the network terminal to act as the required terminating admittance. 'I'he cathode 2| of this tube may be connected to terminal l of the netwofrk. The control grid 22 and the anode 24 may be tied together and connected to the terminal 3. The termination admittance of the network now includes the tube impedance which is in turn a function Of en.

Heretofore no mention has been made of any means for providing any of' the tubes shown with the necessary operating potentials. It is understood of course that these potentials must be provided but it is considered to be a matter of common knowledge how to energize tubes with direct potentials and to block these potentials from any portions of the external circuits in which direct current potentials are undesirable.

One of the operating potentials that is of particular importance in the present invention is the grid bias, for the grids of tubes I0, I0', and l0" of the prior iiguresgwhose value determines the transconductance of the tube. It will of course be understood that when it is desired to vary the phase shift produced by any of the means disclosed in the present invention, this phase shift is most readily controlled by varying simultaneously and equally all the grid biases of the tubes in the phase shifting structure. If at the same time the bias of the terminating tube 20 oi Figure 5 is similarly varied, the termination necessarily is maintained equal to the iterative value required for operation in accordance with the present theory.

v It is not always necessary however to provide a physically distinct tube for a termination. For example. if the network of Figure 4 is terminated by the tube arrangement of Figure 5, the two tubes whose conductances thus fall in parallel,

may be coalesced into a single tube as shown in. Figure 6.

In Figure 6 the final tube 36 has a grid voltage equal to the arithmetic mean of the input voltage er and output voltage e2, that is to say, its voltage is equal to the sum of the two voltages impressed upon the two grids of the two parallel tubes I and that result from connecting Figure 5 to Figure 4. Thus Figure 6 may be looked upon as a terminating network section that may be used alone or connected to the output of a series of other network sections such as shown in Figure 3 or 4. It will be understood, of course, that no appreciable power may be taken from the output terminals of Figure 6 since it is already self loaded by the proper amount.

A very useful special form of the networkof Figure 6 is shown in Figure 7. The network of Figure 7 produces the same phase shift and without amplitude change that is the property of the networks of Figures 3, 4 and 6, but the network of Figure 7 does not have the same input admittance. The network of Figure '7 is particularly well adapted to be used when a source of input voltage is available which is independent of variations of the input impedance of Figure 7. Since Figure 7 is, like Figure 6, self loaded to the proper terminating value, we thus have a phase shifting section involving only a single tube 'l0 yet capable of producing phase shift in alternating current potentials without amplitude change.

Figure 8 illustrates the manner in which the simple phase shifting arrangement of Figure 7 may be embodied in a practical signalling circuit. oscillations are generated by an electron coupled oscillator O whose plate current induces the input voltage e1 in series with the input terminals of a structure of the type shown in Figure '7.

This may be accomplished in any appropriatemanner but is preferably accomplished by coupling the output reactance 80 to a reactance Z which is equivalent to the first impedance Z of Figure '7. Due to the high impedance of the oscillator plate circuit there will be a substantially constant current in 80 regardless of reaction from the phase shifting circuit to the oscillator plate circuit so that the voltage e1 induced in the input of the phase shifter is constant. The output voltage e2 of Figure 7 is connected in Figure 8 to the input electrodes of an amplifier or frequency multiplier tube A which delivers the phase modulated wave energy to any desired utilization circuit directly or by way of additional amplifiers and if desired frequency multipliers. The amount of phase shift imparted to the wave energy in the network is controlled in accordance with a potential which determinesl the operating bias of the phase shifter tube 10. yBlocking condensers 'l2 and 14, grid choke 16 and grid leak 18, and grid screen and plate batteries are supplied as illustrated in the drawings where desired and as desired.

In all of the foregoing no account has been taken of inter-electrode capacities of the screen grid tubes used. If in practice it is found that these capacities interfere with satisfactory operation in any particular case, they may be tuned out or neutralized by such well-known means as paralleling the undesired capacity with induct-` ance having equal reactance value, neutralizing where feasible by means of bridge circuits, or by connecting to the live side of the undesired capacity a section of transmission line whose length is chosen to draw a neutralizing wattless current from the above mentioned live terminal. In addition to undesired capacity there may also appear unavoidable resistance in the reactance elements of these structures. These result in a slight change in the behavior of the structure which may be compensated for by slight changes in the voltage applied to the grid of the tube of the structure. This matter of equalizer arrange ments is well known and Will not require a fuller discussion in order to understand the operation of the present invention.

It will be observed that the phase shift pro'- duced by the circuits, for example that of Figure 8, increases with increasing tube conductance in a fairly linear fashion until the phase shift is of the order of 15 or 20 degrees. As the tube conductance is further increased, however, the phase shift increases more and more slowly. Hence, if it is desired to have the phase shift vary strictly in proportion to the change of operating potential to the grid, it is preferable to construct the grid in such a way that the transconductance of the tube increases more rapidly than in direct proportion to changes of operating grid potential in a. positive direction. By this means the phase shift may be made substantially linear with respect to grid potential over a still wider operating range. The method of constructing a control grid or a screen to produce a predetermined relation between operating grid potential and tube transconductance is well known.

Moreover, in practice a small linear phase modulation accomplished in my network may be increased to a large linear phase modulation by frequency multiplying the energy taken from points 3 and 4 before utilizing the same.

I claim:

1. In a phase shifting network, a pair of conductors having input terminals to which alter- .nating currents may be applied and output terminals from which alternating currents shifted in phase may be taken, an impedance in one of said conductors, a tube having a control grid, an anode, and a cathode, and having its anode to cathode impedance connected in shunt to said conductors, circuit means for applying the potential drop across said impedance to the control grid and cathode of said tube, and an impedance connected across said output terminals, said last named impedance having an admittance equal to the iterative input admittance of said network.

2. In a phase shifting network, a pair of conductors having input terminals to which alternating currents may be applied and output terminals from which alternating currents shifted in phase may be taken, an impedance in one oi said conductors, a tube having a control grid, an anode, and a cathode, and having its anode to cathode impedance connected in shunt to the output terminals of said conductors, circuit means for applying the potential drop across said im pedance to the control grid and cathode of sai', tube, and an impedance connected across sau. output terminals, said impedance having an ac mittance equal to the iterative input adrnittane of said network.

3. In a phase shifting network, a pair of con ductors having input terminals to which alter nating currents may be applied and output te7 minals from which alternating currents shifti'ri .I

in phase may be taken, an impedance in one said conductors, a. tube having a control grid, anode, and a cathode, and having its anode cathode impedance connected in shunt to tl:A input terminals of said conductors, circuit means` ill) fili

iti

for applying the potential drop across said impedance to the control grid and cathode of said tube, and an impedance connected across said output terminals, said impedance having an ad- 5 mittance equal to the iterative input admittance of said network.

4. In a phase shifting network, a pair of parallel .conductors having input terminals to which carrier wave oscillations may be applied and output m terminals from which said-oscillations shifted in phase may be taken, a plurality of impedances in series in one of said conductors, an electron discharge device havinga control grid, an anode, and a cathode, and having its anode to cathode impedance connected in shunt to said conductors, a

circuit for applying the potential drops through said impedances between the control grid and cathode of said device, and an impedance connected across the output terminals of said conductors, said last named impedance having an admittance equal to the iterative admittance of said network.

5. In a phase shifting network, a pair of parallel conductors having input terminals to which alternating current potentials may be applied, said conductors having output terminals from which phase shifted alternating current potentials may be taken, an impedance in one of said conductors,

a pair of tubes each having an anode, a cathode and a control grid, means connecting the anode 3u to cathode impedance of one of said tubes in' shunt to the input terminals of said conductors.

means connecting the anode to cathode impedance of the other of said tubes in shunt to the output terminals of said conductors, a circuit for 3 3 applying the potential drop through said impedance between the control grids and cathodes of said tubes, and an impedance connected across the output terminals of said conductors, said last named impedance having an iterative admittance u equal to the admittance of said network.

6. In a phase modulation signalling system, a network comprising a pair of conductors having input terminals to which alternating current potentials may be applied and output terminals from which phase shifted alternating current potentials may be taken, an impedance in one of said conductors, a tube having a control grid, an anode and a cathode, means for applying alternating current potentials to be modulated between the control grid and cathode of said tube, a circuit connecting the control grid and anode of said tube in shunt to said impedance in said one of said conductors for exciting both electrodes by alternating current potentials from said impedance, an output circuit connected with the output terminals of said conductors, and means for applying signal potentials to the control grid of said tube.

7. In a phase shifting system, a plurality of phase shifting network vsections connected in series, each network having a terminal admittance equal to its iterative admittance, means for applying varying potentials to be shifted in phase to the first of said networks and for deriving varying potentials shifted in phase from the last of said networks, means for varying the iterative admittance of each section to thereby vary the phase of the potentials in the sections and means for simultaneously varying the terminating adn mittance of each section to keep it equal to the varying iterative admittance of the sections.

8. A phase shifting network comprising series impedance between input terminals to which alternating currents may be applied and output l terminals from which phase shifted currents may auaaeo be taken, an electron discharge device impedance shunted across said input terminals, an electron discharge device impedance shunted across said output terminals, and means for applying an alternating current potential to a control electrode in each of said devices equal to one half the difference between the input current potentials and output current potentials.

9. An alternating current phase shifting network comprising two reactance elements in series and an electron discharge device shunted across said network between said reactance elements,

said network having input terminals on which alternating current voltage may be impressed and having output terminals, a second electron discharge device having an admittance equal to the admittance of said first named device connected with said output terminals, means for varyingthe transconductances of said devices equally to produce a phase shift between the input alternating current voltage and the output alternating current voltage without change of amplitude, said phase shift being substantially proportional to the transconductance of said devices.

l0. In means for adjusting the' phase of alternating voltages, an alternating voltage phase shifting network section having input and output terminals, a pair of reactances in series between said network input and output terminals and a tube having a control grid and having an anode and cathode in shunt relation to said network at the Junction of said reactances, and means for exciting the grid of said tube by a voltage equal to the difference between the input and output voltages of said network section.

11. In a cascaded arrangement of alternating current phase shifting networks each comprising reactance of a single sign and an electronic transconductance device and each having the same iterative admittance, the said arrangement being terminated by electronic admittance equal to the iterative admittance of the component networks, said networks including means for varying said electronic transconductances and electronic admittance whereby to vary the amount of phase shift per network, the method of producing relatively large phase shift in accordance with signalling voltages which consists in simultaneously varying at signal frequency the transconductance of said device, to thereby vary the amount of phase shift produced by each cascaded network, and the terminating admittance of said cascaded network.

l2. The combination of reactance of a single sign and an electronic transconductance device to form a network for shifting phase without varying amplitude, and an electronic transconductance device connected to said network to provide a terminating admittance equal to the iterative admittance of said network, and means for simultaneously varying the transconductance of said first named device in accordance with signalling voltages and the transconductance of said second named device to maintain the terminating admittance of said network at all times equal to its iterative admittance.

13. In means for modulating the phase of alternating voltages at signal frequency without modulating the amplitude of said voltages, a pair of network sections connected in series, each network comprising an impedance and having terminating admittances equal to their input iterative admittance, an electron discharge device connected in shunt to the adjacent terminals of said networks, means for varying the impedances oi Uil said devices at signal frequency, and means for applying alternating voltages to the input of the first network.

14. In a phase modulation system, a complex phase shifting network having input'and output terminals, an impedance in shunt to one set of said terminals, said impedance having an admittance equal to the iterative admittance of said network, a tube having its internal impedance connected across said network, and means for varying the impedance of said tube in accordance with signalling potentials.

15. In a system for shifting the phase of a1- iterative admittance.

ternating current voltages while maintaining the amplitude of said alternating current voltages constant, a network including at least three circuit elements, at least one of which circuit elements is an electron discharge amplier tube having anode, cathode, and control electrode and at least one of which elements isa passive reactance, the elements being so connected that the iterative admittance of said network is equal to the transconductance of said tube, said network being terminated by an admittance equal to its WALTER van BQROBERTS. 

